‘Killer mice’ wreak havoc on Marion Island

Published May 9, 2015


Durban - On a small volcanic island almost 2 000km south of Durban, house mice are wreaking ecological havoc in one of South Africa’s most unspoiled wilderness areas.

The mice have been on Marion Island since the early 1800s – long before the island was annexed by the South African government in 1947.

Now, almost 200 years later, the Birdlife SA conservation group is leading an initiative that could rid the island of the “killer mice” once and for all.

“Marion Island is the jewel in the crown of South Africa’s islands,” said Ross Wanless, the head of Birdlife’s seabird conservation programme.

“It is massive, beautiful, and a sanctuary for seabirds, seals, killer whales and more.”

The problem, however, is that mice have colonised almost every corner of the 290km2 island, which was declared a Special Nature Reserve in 1995.

Apart from eating rare and endangered seabirds, the mice also damage rare vegetation such as the pincushion plant.

“We know they eat albatross chicks, flightless moths and a wide range of species that are integral to the whole ecosystem.”

Wanless said mice had reached densities of up to 200 a hectare, suggesting that there were now “a couple of million” of them spread across the island.

Nearly 75 years ago, an attempt was made to solve the mouse problem by introducing some domestic cats – but this turned out to be a disaster.

From an initial population of one castrated tabby cat, a single female and three kittens introduced in 1949, the cat population exploded.

In 1975, nearly 2 000 feral cats ate almost half-a-million birds and caused the extinction of three petrel species.

To eradicate them, managers introduced a cat-specific disease to the island and also hired teams of marksmen who shot more than 800 cats with 12-bore shotguns.

All told, it took 19 years to get rid of the last cat on Marion Island, and this is why Birdlife is anxious to solve the mice problem quickly.

The good news, said Wanless, was that new mouse eradication techniques had been refined in South Georgia and Australia’s Macquarie Island.

“The bad news is that these are fiendishly expensive, risky operations that require extensive studies, exquisite planning and a lot of time.”

The first step is to hire John Parkes of New Zealand to conduct an expert study on the island, which includes whether there are significant risks to other species and other logistical problems from using poisoned pellets.

Now Birdlife is hoping to raise R200 000 to cover the expense of getting Parkes to the island to conduct a feasibility study and risk assessment.

Wanless said most sea birds were not susceptible to poisoned cereal pellets, although some could be vulnerable.

“There will be some collateral damage, but much of this can be avoided by hitting the mice hard when most of the vulnerable species are not present on the island.”


l For further information on supporting the mouse eradication project, contact Wanless at 021 419 7347 or e-mail: [email protected]

The Mercury

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